European Rugby Cup announced the verdict on Friday following a disciplinary hearing in Dublin.
Gloucester lodged the citing complaint under tournament rules that allow clubs to make protests following Challenge Cup games that are not broadcast live on television and do not always see a citing commissioner appointed.
Independent citing officer Gordon Black then decided there were grounds to convene a disciplinary hearing.
Mark McParland, an independent judicial officer, upheld the citing complaint and determined that 23-year-old prop Phelipponneau, who pleaded not guilty, had struck England Saxons squad member Knight with two punches to the head.
He cannot play again until February 18.
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